Methods and apparatus for automatic scanner calibration

ABSTRACT

An automatic scanner calibration method and apparatus is disclosed in which a calibration target, such as a Kodak® gray strip, is attached to a scanning surface of a scanner. During a normal scan, the calibration target area can be ignored or scanned depending on user selection. If the calibration target is scanned, then the resulting information is used to calibrate the scanner automatically. Such calibration is more accurate than an older in time or preset default calibration. Another embodiment of the invention actuates a print of a printer calibration target on a printer on a scheduled basis. Thereafter, the user can take the printer calibration target and place it on the scanner and perform a calibration of a scanner/printer system.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/976,880, filed 11 Oct. 2001, now U.S. Pat. No. 7,212,312, which is acontinuation of U.S. patent application Ser. No. 09/235,642, filed 22Jan. 1999, now U.S. Pat. No. 6,327,047.

BACKGROUND

The invention relates to the calibration of a scanner. Moreparticularly, the invention relates to methods and apparatus forautomatically calibrating a scanner. Another embodiment of the inventionrelates to automatically calibrating a printer.

Many scanning and printing technologies are complex and, due to manydifferent physical and environmental factors, may drift in their colorresponse. For example, in the case of a scanner, the quality of lightproduced by the light source drifts over time due to the gradualvariation of both electronic and optical components of the scanner. Inthe case of a printer, the amount of color toner or ink that is printedon paper changes over time. It is preferable that printers and scannershave a steady and consistent color response.

Prior art systems attempt to compensate for the difference in colorbehavior between a measured response of the printer or scanner and anideal response of the printer or scanner by various calibratingtechniques. One common way to calibrate a scanner involves scanning acalibrated target strip with a scanner and then using software thataccompanies the calibrated target strip to perform the calibration. Thesoftware measures density values on the strip and compares the measuredvalues to stored density values known to correspond to the calibratedtarget strip. The software generates modified or calibrated densityvalues and typically stores the calibrated values in an associationtable known in the art as the lookup table (“LUT”). More expensivescanners are capable of running the software, while less expensivescanners run such software on an associated personal computer (“PC”).

Common in the art are two types of calibrated target strips that comewith color management software and that can be purchased on the market.The two common strips are the Kodak® Gray Scale calibrated target stripproduced by the Eastman Kodak Corp. of Rochester, N.Y. and theANSI-standard IT8 target manufactured by, for example, the AgfaDivision, Bayer Corporation. The Kodak® Gray Scale comprises patches ofvarying densities of gray and the IT8 strips comprise color patches.

It is known to calibrate a color image reproduction system by generatinga scanner calibration table and a printer calibration table. However,the method is elaborate in that it includes the steps of providing a setof calibration tools that are developed on a separate representativesystem and the steps of applying the calibration tools to calibrate thecolor image reproduction system. Such a system is described in Wan etal. U.S. Pat. No. 5,452,112.

Dietz et al. U.S. Pat. No. 5,689,110 (“Dietz”) discloses a method andapparatus for calibrating a specialized optical scanner known as afluorescence spectrometer. One of the apparent significant applicationsof a fluorescence scanner is in the field of medicine wherein, forexample, a blood sample is mixed with a fluorescence dye, and the bloodsample is scanned and analyzed to determine certain cellcharacteristics. The calibration method and apparatus disclosed in Dietzinvolves such techniques as calibrating to calibration standards, suchas gold and rubies, and is not directly relevant to the type of colorimage scanner addressed in this document.

Quardt et al. U.S. Pat. No. 5,194,966 (“Quardt”) discloses a method foroptimizing optical scanners by automatically determining imageprocessing threshold values using a threshold image calibration sheet.One embodiment comprises the steps of repetitively scanning the sheetuntil scanner threshold values are determined. Another embodimentcomprises the step of a single scan but uses two or more scanner camerasto work together to process the document images. The method disclosed inQuardt requires a significant amount of labor to complete repetitivescans and/or requires a scanning device having two or more cameras.

Sherman et al. U.S. Pat. No. 5,537,516 (“Sherman”) discloses a methodfor calibrating a subject scanner that uses a standard target withrespect to a calibrated reference scanner, known as the object scanner.The method generates scanner correction tables for the readings of thesubject scanner. The output of the object scanner when scanning areference target is compared to the output of the subject scanner whenscanning the reference target. This method requires a deliberate actionon the part of a user whenever calibration is desired in which the useris required to have the target on hand and the user is required to scanthe target. Sherman further provides an improved method of measuring inkdensities using a subject scanner. In one embodiment, a target is placedat a defocused point with respect to a focal point of the scanningdevice, and in an alternate embodiment, a diffusing substrate ratherthan a defocusing means is placed between a target and the scanningdevice.

It is also known to generate a scanner profile by scanning a standardgray scale test strip comprising a plurality of gray scale patches andcomparing the scanned test strip data to a stored data file containingdensity values known to correspond to the test strip. Such a method isdescribed in Falk U.S. Pat. No. 5,760,913 (“Falk”), which discloses theuse of a scanner as a densitometer to calibrate a printer. As in some ofthe previously described documents, the method and system taught by Falkrequires the user to have the standard gray scale test strip or itsequivalent readily available and requires the user to scan a calibrationtarget and a test strip on the scanner to perform the desiredcalibration process.

It would be advantageous to provide an automatic scanner calibrationmethod and apparatus. For example, a user who must perform a calibrationof a scanner may have misplaced a calibrated target strip. In the priorart, calibration cannot be performed if a target strip is misplaced.

It would also be advantageous for an automatic scanner calibrationmethod and apparatus to provide a means by which a user can calibratethe scanner during a normal scan of an object. An automatic scannercalibration method and apparatus providing the means to calibrate thescanner during a normal scan of an object has the potential to be moreaccurate than older in time calibrations and more accurate than ascanner set to the preset default settings provided by the manufacturer.For example, it is well known in the art that a scanner can have a warmup time of about twenty minutes before reaching a steady output value. Auser may desire to scan an image prior to a scanner reaching the steadyoutput value. It would be advantageous for the user to calibrate thescanner automatically.

SUMMARY

Methods and apparatus in accordance with this invention provide acalibration target that a user attaches once to any of an inside surfaceof a scanner glass, an outside surface of a scanner glass, or to aninside of a scanner cover. During a normal scan of an object, the usercan select to ignore the calibration target or can select to scan thecalibration target. If the calibration target is scanned, then thescanner is calibrated automatically during the scan of the object.

An exemplary calibration target is about one-quarter of an inch toone-half of an inch wide and generally has a length that isapproximately equal to the length or the width of the platen of thescanner. Standard manufactured calibration targets can be purchased andused in the invention.

The calibration target strips also can be customized to suit acombination of needs. For example, the calibration target can comprise adecal that easily adheres to the scanner glass. The calibration targetcan adhere to the scanner in a variety of other ways. For example, thecalibration target can slip into a plastic non-reflective sleeve, wherethe sleeve is attached to the inside of the scanner cover.

An alternate embodiment of the invention is provided that also comprisesautomatically calibrating a printer using a scanner. A print of aspecial printer calibration target is automatically actuated on theprinter and a message is generated to ensure that the special printercalibration target is placed on the scanner. The special printercalibration target has interpretable data that represents the printer tobe calibrated, the associated printer controller engine, and the datethe target is printed. The interpretable data on the special printercalibration target can be embedded in a barcode using barcodetechnology.

To calibrate the printer the special printer calibration target isscanned on the scanner. During the scan the of special printercalibration target, the user can select also to calibrate the scanner.The calibration target attached to the scanner is scanned and thescanner is automatically calibrated before the automatic calibration ofthe printer without any additional effort by the user.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present invention can be more clearly understood fromthe following detailed description considered in conjunction with thefollowing drawings, in which the same reference numerals denote the sameelements throughout, and in which:

FIG. 1A is a block schematic diagram of the calibration system accordingto the invention;

FIG. 1B is a block schematic diagram of the calibration system accordingto the invention;

FIG. 2A is a top view of a calibration target strip disposed on ascanner glass according to the invention;

FIG. 2B is a top view of a calibration target strip disposed on aninside cover of a scanner according to the invention;

FIG. 3 is a reproduction of a calibration target strip;

FIG. 4 is another reproduction of a calibration target strip;

FIG. 5 is a flow diagram showing a method for automatically calibratinga scanner according to the invention;

FIG. 6A is a block schematic diagram of an alternative calibrationsystem according to the invention;

FIG. 6B is a block schematic diagram of an alternative calibrationsystem according to the invention;

FIG. 7 is a flow diagram showing a method for automatically calibratinga printer and automatically calibrating a scanner according to theinvention; and

FIG. 8 is a pictorial illustration of a printer calibration targethaving a barcode according to the invention.

DETAILED DESCRIPTION

This invention provides an automatic scanner calibration method andapparatus which includes a calibration target strip that, in thepresently preferred embodiment of the invention, a user attaches once toany of an inside surface of a scanner glass, an outside surface of ascanner glass, or an inside of a scanner cover. During a normal scan ofan object, the user can select to ignore the calibration target strip orcan select to scan the calibration target strip. If the calibrationtarget strip is scanned, then the scanner is calibrated automaticallyduring the scan of the object.

In the preferred embodiment of the invention, the calibration targetstrip generally is about one-quarter of an inch to one-half of an inchwide and generally has length that is approximately equal to the lengthor the width of the platen of the scanner. Standard manufacturedcalibration target strips can be purchased and used in the invention.

The strip also can be customized to suit a combination of needs. Forexample, the strip can comprise a decal which easily adheres to thescanner glass. The strip can also be adhered to the scanner in a varietyof other ways. For example, the strip can slip into a plasticnon-reflective sleeve where the sleeve is attached to the inside of thescanner cover.

An alternate embodiment of the invention is provided that also comprisesautomatically calibrating a printer using a scanner. A print of aspecial printer calibration target is automatically actuated on theprinter and a message is generated to ensure that the special printercalibration target is placed on the scanner. The special printercalibration target has interpretable data that represents the printer tobe calibrated, the associated printer controller engine, and the datethe target is printed. In one embodiment of the invention, theinterpretable data on the special printer calibration target can beembedded in a barcode using barcode technology. To calibrate the printerthe special printer calibration target is scanned on the scanner. Duringthe scan the of special printer calibration target, the user can selectalso to calibrate the scanner. The calibration target strip attached tothe scanner is scanned and the scanner is automatically calibratedbefore the automatic calibration of the printer without any additionaleffort by the user.

FIG. 1A shows a block diagram of an apparatus for practicing a presentlypreferred embodiment of the invention is shown. A client engine 10 iscoupled to a scanner controller engine 20. The scanner controller engine20 is coupled to the scanner 30. In one embodiment of the invention, theclient engine 10 is a PC and the scanner controller engine 20 issoftware residing on the PC that controls a scanner 30 connected to thePC 10. In this embodiment, a user can scan an image on the scanner 30 byinteracting with scanner software 20 on the PC 10.

Another block diagram of system for performing calibration in accordancewith the invention is shown in FIG. 1 b. A first client engine 50 iscoupled to a first scanner controller engine 60. The first scannercontroller engine 60 is coupled to a second scanner controller engine 70by a network connection 80. The second scanner controller engine 70 iscoupled to a scanner 90. In an embodiment of the invention, the clientengine 50 is a PC, the first scanner controller engine 60 is softwareresiding on the PC, the second scanner controller engine 70 is softwareresiding on what is generally known to anyone in the art as a network,the first scanner controller engine 60 is coupled to the second scannercontroller engine 70 by a typical network connection 80, and the secondscanner controller engine 70 is coupled to a scanner 90 on the network.In this embodiment, a user can scan an image on the scanner 90 on thenetwork by interacting with scanner software 60 on the PC 50.

The scanner software on the PC 60 comprises a user interface to thescanner controlling software 70 on the network. It will be apparent to aperson skilled in the art that this embodiment of the inventionparticularly addresses what are currently expensive scanners that haveembedded scanner controlling software and many varieties of scanners,including for example a copier that is self-contained, containing aninterface to the user, as well as a scanner controller engine. The termscanner, as used herein, refers generally to a device for converting,for example, pictures, artwork, documents, transparencies, andphotographs, into electronic form.

FIG. 2A is a top view of a calibration target strip 200 disposed on asurface of a scanner glass 210 according to the invention. In oneembodiment of the invention, the target strip 200 is made of decalpaper. Other embodiments may include a target strip made of a materialthat adheres to the glass by static attraction or by “weak” adhesives,such as are used in Post-Its® manufactured by BM Corporation ofMinneapolis, Minn. The adherence mechanism should not possess opticalqualities that distort the colors of the target strip. The strip 200 isadhered to the glass 210. The strip 200 can remain on the glass 210until a user decides to peel it off. The user does not have to worryabout losing the strip and the strip is readily available when the userdesires to calibrate the scanner.

Many variations on the properties of a calibration target strip 200 arepossible according to the invention. For example, the calibration targetstrip can be a photograph on photographic paper. The calibration targetstrip can be made of a dye sublimation print on photographic paper or ona paper equivalent to photographic paper. The calibration target stripcan be made of a plastic material, wherein the plastic material has anadhering surface, and a covering over the surface, such that theadhering surface allows the plastic material to adhere to the top of thescanner glass, the bottom of the scanner glass, or the inside of thecover of the scanner when the covering is removed from the adheringsurface. The plastic material can have a dye sublimation print printedon it. A user can apply a protective coating such as, for example, anultra-violet resistant coating or a scratch resistant coating, to thecalibration target strip prior to attaching the strip to the top of thescanner glass, the bottom of the scanner glass, or the inside of thecover of the scanner.

Manufactured calibration target strips can be purchased and used in theinvention. Two examples of manufactured calibration target strips wellknown to a person skilled in the art are a Kodak Gray Strip by theEastman Kodak Corporation of Rochester, N.Y. and the ANSI-standard IT8target manufactured by, for example, the Agfa Division, BayerCorporation (see FIGS. 3 and 4). One embodiment of the invention uses apurchased calibration target strip in a scanner that has a tray devicelocated at the scanner glass or located at the inside of the scannercover, such that the calibration target strip can be slipped into thetray so that it remains fixed until the user decides to remove thestrip. The tray device according to the invention can hold a variety oftypes of targets in addition to manufactured targets. In anotherembodiment of the invention, the scanner has a plastic non-reflectivesleeve located at the scanner glass or located at the inside of thescanner cover such that a calibration target strip can be slipped in theplastic non-reflective sleeve.

Sometimes it is necessary for a user to use the entire scanning range ofa scanner when scanning an object. Herein, the scanning range comprisesa first surface area that spans a part of or all of the glass of thescanner and a second surface area that extends beyond the first surfacearea of the scanning range. Refer to FIG. 2B, which is a top view of acalibration target strip 220 disposed on an inside cover 230 of ascanner 240 according to the invention. In this embodiment of theinvention, a calibration target strip 220 is attached to the inside ofthe cover 230 of the scanner 240 in such a way that the calibrationtarget strip 220 is not fully overlapping any part of the first surfacearea of the scanning range but is overlapping a part of or all of thesecond surface area of the scanning range. An object covering the entirescanning glass and the calibration target strip itself can both bescanned. In another embodiment of the invention, the calibration targetstrip can be attached to the inside of the cover of the scanner.

In a preferred embodiment of the invention, the calibration target striphas a width of approximately one-quarter on an inch or one-half of aninch and a length approximately equal to a length or a width of a platenof a scanner. These dimensions of the calibration target strip ensurethat the calibration target strip occupies the least amount of thescanning range as possible so that as much of the scanning range aspossible can be used for scanning objects.

FIG. 5 shows a flow diagram for automatically calibrating a scanneraccording to the invention. A calibration target strip is attached tothe inside surface of the scanner glass, the outside surface of thescanner glass, or the inside of the cover of the scanner (300). Thisstep (300) is performed once. A user desires to scan an object on thescanner and initiates the scanning process (301). The user places theobject on the scanner (302). By an interactive means with the scannercontroller engine, the user decides whether the scanner is to becalibrated or not (303). If the user wants the scanner to be calibrated,the calibration target strip is automatically scanned (304). Then thescanner controller engine performs the calibration on the scanner usingthe calibration target strip and generates calibrated values (305). Theobject is scanned using the updated calibrated values (306). If the userdoes not want the scanner to be calibrated, then steps (304) and (305)are ignored and the object is scanned using the current calibratedvalues (306). If the user has no more objects to scan (307), the processends (308). Otherwise, the process is repeated (301). If the userdesires, the user can calibrate the scanner for every single scan. Theuser can decide not to calibrate during a scan if it is more importantto the user to perform the scan quickly rather than take the time tocalibrate the scanner.

FIG. 6A shows a block diagram of an apparatus for automaticallycalibrating a scanner and for automatically calibrating a printer. Aclient engine 400 is connected to a printer 401 over a networkconnection 402 using a printer controller engine 403 that is coupleddirectly to the printer 401 and to the network connection 402. Theclient engine 400 is also connected to a scanner 404 using a scannercontroller engine 405 that is coupled directly to the client engine 400and the scanner 404. In one embodiment of the invention, the clientengine 400 is a PC and the scanner controller engine 405 is softwareresiding on the PC that controls a scanner 404 that is connected to thePC 400. The PC 400 is connected over the network connection 402 to aprinter 401 on the network. The printer controller engine 403 isimplemented in software that resides on the network which controls theprinter 401.

FIG. 6B shows a block diagram of an apparatus for automaticallycalibrating a scanner and for automatically calibrating a printer. Aclient engine 406 is connected to a printer 407 over a networkconnection 408 and the client engine 406 is connected to a scanner 409over a network connection 408. The client engine 406 is coupled to theprinter 407 and the scanner 409 using a multi-function scanner/printercontroller engine 410 that is coupled to the network connection 408 andthat is coupled directly to the printer 407 and to the scanner 409. Theclient engine 406 is a PC and the multi-function scanner/printercontroller engine 410 is implemented in software which resides on thenetwork that controls the printer 407 and the scanner 409.

FIG. 7 shows a flow diagram for automatically calibrating a printer andautomatically calibrating a scanner. A client engine initiates ascheduled first message to a printer controller engine to print aprinter calibration target (500). The schedule can be set according tothe convenience of the user such as, for example the schedule caninitiate a print each night. Upon completion of the print of the printercalibration target on the printer, the printer controller engineindicates by posting a second message to the client engine that theprinter calibration target has been printed and further indicates by thesame second message that the printer calibration target should be placedon the scanner (501). The printer controller engine waits for the clientengine to respond that the printer calibration target is placed on thescanner (502). The step to scan the printer calibration target isinitiated (503). In this embodiment of the invention, a calibrationtarget strip is attached to the scanner and is scanned during thescanning of the printer calibration target. A multi-functionscanner/printer controller engine calibrates the scanner and calibratesthe printer by updating a LUT for the scanner and updating a LUT for theprinter (504). The process illustrated in FIG. 5 provides a mechanism toensure that the printer is calibrated on a regular basis withoutdepending on a user to remember to calibrate the printer. A similarmechanism may be used to automatically calibrate the scanner inaccordance with the embodiment of the invention discussed above.

In another embodiment of the invention, the print of the printercalibration target can be started simultaneously on multiple printers byone software/scanner combination. The operator may then place theprinted calibration targets in any order either on the scanner glass orinto the scanner's automatic document feeder.

FIG. 8 shows a pictorial illustration of an example of a printercalibration target having a barcode. The target has two columns 600 and601 of the single ink colorants, cyan, magenta, yellow, and black. Theleft-hand column 600 has the single ink colorants in the order, cyan602, magenta 603, yellow 604, and black 605 from left to right. Thecolumns of single ink gradually decrease in density from full ink to noink. The left-hand column 600 has density values decrease from the toppart of the target to the bottom part of the target. The right handcolumn 601 is organized similarly with some items in the reverse order.The right hand column 601 has the single ink colorants in the order,black 606, yellow 607, magenta 608, and cyan 609 from left to right. Thecolumns of single ink gradually increase in density from no ink to fullink. The right hand column 601 has density values increase from the toppart of the target to the bottom part of the target. In the preferredembodiment of the invention, a barcode 610 is printed on the target, thebarcode contains data that identify the printer on which the target wasprinted, the printer controller engine associated with the printer onwhich the target was printed, and the date the target was printed. Thoseskilled in the art will appreciate that other information may be printedon the target and that the indicator by which the information isrecognized is not limited to bar codes (although a bar code-likemechanism stores information in format that is readily recognized whenscanned by the scanner).

The foregoing merely illustrates the principles of this invention, andvarious modifications can be made by persons of ordinary skill in theart without departing from the scope and spirit of this invention.

1. A computer-implemented method for use with a scanner, the methodcomprising: scanning, with a scanner, a calibration target, which isaffixed to the scanning surface, and an object, which is placed on saidscanning surface at the same time; wherein the scanning step furthercomprises the step of calibrating, with a computer, the scanner usingthe calibration target and generating, with the computer, calibrationvalues using the calibration target; wherein the object is scanned usingthe generated calibration values; and wherein the calibration targetcomprises any of (a) patches of varying densities of gray and (b) colorpatches.
 2. The method of claim 1, wherein the scanner comprises aplaten having a length, and the calibration target comprises a lengththat substantially equals the length of the platen.
 3. The method ofclaim 1, wherein the scanner comprises a platen having a width, and thecalibration target comprises a length that substantially equals thewidth of the platen.
 4. The method of claim 1, wherein the calibrationtarget comprises a manufactured calibration target.
 5. The method ofclaim 1, wherein the calibration target comprises a photograph.
 6. Themethod of claim 1, wherein the calibration target comprises a dyesublimation print.
 7. The method of claim 1, wherein the calibrationtarget comprises a plastic material, the plastic material having anadhering surface and a covering over the adhering surface such that theadhering surface allows the plastic material to adhere to a part of thescanner when the covering is removed from the adhering surface.
 8. Themethod of claim 1, wherein the calibration target comprises a dyesublimation print onto a plastic material, the plastic material havingan adhering surface and a covering over the adhering surface such thatthe adhering surface allows the dye sublimated plastic material toadhere to a part of the scanner when the covering is removed from theadhering surface.
 9. The method of claim 1, further comprising providinga calibration target having a protective coating.
 10. The method ofclaim 1, wherein the calibration target comprises decal paper.
 11. Themethod of claim 1, wherein the scanner further comprises a plasticnon-reflective sleeve located proximate to a scanning surface forfixedly holding the calibration target.
 12. Apparatus for use with ascanner, the apparatus comprising: a calibration target; a means forattaching the calibration target to a scanning surface of the scanner;the scanner for scanning the calibration target and an object; a meansfor calibrating the scanner during a normal scan of the object, saidmeans for calibrating using the calibration target; and a means forgenerating calibration values; wherein the object is scanned using thegenerated calibration values; and wherein the calibration targetcomprises any of (a) patches of varying densities of pray and (b) colorpatches.
 13. The apparatus of claim 12, wherein: the scanner furthercomprises a platen comprising a length; and the calibration targetcomprises a length substantially equal to the length of the platen. 14.The apparatus of claim 12, wherein: the scanner further comprises aplaten comprising a width; and the calibration target comprises a lengthsubstantially equal to the width of the platen.
 15. The apparatus ofclaim 12, wherein the calibration target comprises a manufacturedcalibration target.
 16. The apparatus of claim 12, wherein calibrationtarget comprises a photograph.
 17. The apparatus of claim 12, whereinthe calibration target comprises a dye sublimation print.
 18. Theapparatus of claim 12, wherein the calibration target comprises aplastic material, the plastic material having an adhering surface and acovering over the adhering surface such that the adhering surface allowsthe plastic material adhere to the scanner when the covering is removedfrom the adhering surface.
 19. The apparatus of claim 12, wherein thecalibration target comprises a dye sublimation print onto a plasticmaterial, the plastic material having an adhering surface and a coveringover the adhering surface such that the adhering surface allows the dyesublimated plastic material to adhere to a part of the scanner when thecovering is removed from the adhering surface.
 20. The apparatus ofclaim 12, wherein the calibration target has a protective coating. 21.The apparatus of claim 12, wherein the calibration target comprisesdecal paper.
 22. The method of claim 1, wherein the scanner iscalibrated during every scan of an object.
 23. The apparatus of claim12, wherein the scanner is calibrated during every scan of an object.